Method and apparatus for manufacturing hollow tubular members

ABSTRACT

There is disclosed a method and apparatus for adjusting the thickness of a hollow tubular member to provide a cross-section of constant area, such adjustment being inversely dependent upon detected increases or decreases in the thickness of the metal strip. The method and apparatus provide for the formation and welding of a metal strip into a hollow tubular member; the application of longitudinally directed, braking or pushing forces to the hollow tubular member; and then the continuous reduction of the hollow tubular member to achieve a cross-section of constant area.

The invention relates to method and apparatus for manufacturing a hollowtubular member whose thickness is adjusted to achieve a cross-section ofconstant volume. Further, the invention relates to such a hollow tubularmember formed as a metalic sheath around a cable core.

BACKGROUND OF THE INVENTION

It is priorly known to manufacture hollow tubular members (for example,wave guides and cable sheaths) by the steps of continuously drawing ametal strip in a longitudinal direction through a plurality of formingrolls to form a hollow tubular member, and then continuously welding thelongitudinal abutting edges of the hollow tubular member. Further, withrespect to cable sheath, it is known to form the metal strip around acable core prior to the step of continuously welding the longitudinalabutting edges of the sheath.

Often wave guides and cable sheaths manufactured in accordance with thepriorly known method and apparatus have been found to have deleteriousdeviations in their thickness along their longitudinal axes. In themain, such deviations were reflections of deviations in thickness of themetal strip employed. Since it was technically impossible to insist upona supply of metal strip of constant thickness, there was a need foravoiding such deviation reflections.

As to cable sheaths for submarine cables there is a requirement that thecable sheaths have a cross-section of constant area, and that the cablesheath and the cable core be tangentially and longitudinally anchored toeach other so as to present an extended unitary structure. Submarinecables referred to herein are of the type that may include a coppersheath, and a cable core comprised of a plurality of electrical andoptical conductors having a plurality of steel wires strandedconcentrically around them for tension reinforcement.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a novel method andapparatus for adjusting the thickness of a hollow tubular member toachieve a cross-section of constant area.

Another object of the present invention is to provide a novel method andapparatus for forming the aforesaid hollow tubular member as a metalicsheath around a cable core.

Still another object of the present invention is to provide a novelmethod and apparatus for forming the aforesaid metalic sheath around thecable core so as to provide tangential and longitudinal anchoringbetween the metalic sheath and the core.

A further object of the present invention is to achieve the aforesaidtangential and longitudinal anchoring by continuously reducing themetalic sheath into engagement with the cable core, while avoidingtorsion in the sheath created by such engagement from being transmittedback through the metalic sheath to a position whereat the oppositelongitudinal edges of the sheath are being welded to each other.

A still further object of the present invention is to provide a novelmethod and apparatus for adjusting the thickness of the aforesaid hollowtubular member by applying longitudinally directed braking or pushingforces to the hollow tubular member, without generating torsional forceswithin the hollow tubular member that would be deleterious to thewelding of the longitudinal abutting edges of such member.

SUMMARY OF THE INVENTION

These and other objects of the present invention are achieved by amethod and apparatus for adjusting the thickness of a hollow tubularmember to provide a cross-section of constant area, such adjustmentbeing inversely dependent upon detected increases or decreases in thethickness of the metal strip from which the hollow tubular member isformed.

The novel method of the present invention comprises the steps ofmeasuring the thickness of the metal strip; drawing and forming themetal strip into a hollow tubular member; and welding the longitudinalabutting edges of the hollow tubular member. Further, such methodincludes the steps of applying longitudinally directed, braking orpushing forces to the hollow tubular member; while continuously reducingthe hollow tubular member, thus producing a cross-section of constantarea.

The novel apparatus of the present invention comprises a source of metalstrip; a means for continuously drawing the metal strip in alongitudinal direction; a measuring device for measuring the thicknessof the metal strip; and forming means and welding means for forming themetal strip into a hollow tubular member and then welding thelongitudinal abutting edges thereof. Further, such apparatus includes acapstan means for applying braking or pushing forces to the hollowtubular member; a servo means coupled between the measuring device andthe capstan means for controlling the aforesaid braking or pushingforces; and a draw down means for reducing the hollow tubular member toa cross-section of constant area.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention as well as the objectsand advantages thereof will become apparent upon consideration of thefollowing detailed disclosure thereof, especially when taken with theaccompanying drawings; wherein:

FIG. 1 is a diagrammatic representation of apparatus for manufacturingimproved cables.

FIG. 2 is an enlarged cross-sectional view of a partially fabricatedcable being manufactured with the apparatus of FIG. 1, as viewed on lineA--A.

FIG. 3 is a cross-sectional view of the partially fabricated cable beingmanufactured with the apparatus of FIG. 1, as viewed on line B--B.

FIG. 4 is an enlarged scale view of a portion of the cross-sectionalview of the partially fabricated cable depicted in FIG. 3.

Referring to FIG. 1, a cable core 1 comprised, for example, of aplurality of electrical and optical conductors longitudinally fed from asupply drum (not shown) toward and into a intermediate position of aplurality of forming rolls 7 positioned within a core sheathing station3. Simultaneously a copper strip 5 is drawn from a supply roller 4,passed through a decreasing bath 6, and fed into an input side of theplurality of forming rolls 7. The spacial positioning of the formingrolls 7, the curvature of the individual roll, the outer diameter of thecable core 1, and the thickness and width of the copper strip 5 are suchas to form the copper strip 5 into a closed tubular sheath 5'concentrically positioned around the cable core 1 prior to the cablecore 1 exiting from the output end of the core sheathing station 3.Positioned in the vicinity of the output end of the core sheathingstation 3 is a welding station 8 for welding adjacent longitudinalabutting edges of the closed tubular sheath 5' as such edgesprogressively pass through the welding station. The welding station 8employs well known argon arc welding procedures conducted in an inertgas environment.

As illustrated by FIG. 2, which is an enlarged cross-sectional view of apartially fabricated cable being manufactured with the apparatus of FIG.1 as viewed on line A--A, the cable core 1 comprises a plurality ofelectrical and optical conductors 2 and a plurality of steel wires 2'stranded over the outer surface of the plurality of electrical andoptical conductors. At line A--A, the outer diameter of the cable core 1(i.e., the outer surface of concentrically formed plurality of strandedsteel wires 2') is less than the inner circular surface of the closedtubular sheath 5'. Consequently, as the cable core 1 progressivelypasses through the welding station 8, the adjacent longitudinally edgesof the closed tubular sheath 5' which are seam welded in a known manner,are spaced a radial distance from the outer surface of the plurality ofstranded steel wires 2'.

Downstream of the welding station 8 are successively: a caterpillarcapstan station 9; a turk's head, sheath reducing station 11; a drawdown station 12; a cable draw apparatus 13; and a wind-up drum 14.

The capstan station 9 is of a prior known type (see for example, U.S.Pat. Nos. 3,085,729; 3,116,865; and 3,128,930) for periodically grippingand tranversely moving the closed tubular sheath 5' in a longitudinalpath. There is included in the capstan station 9 a plurality of gripperassemblies 10 each including a pair of clamping elements (not shown) forengaging and disengaging the longitudinally moving closed tubular sheath5'. Further, capstan station 9 includes drive apparatus (not shown) formoving each of the gripper assemblies 10 in an elongated endless path.Each of the gripper assemblies 10 periodically engages a portion of theouter circumferential surface of the closed tubular sheath 5' in amanner to avoid crushing of the freshly welded sheath, yet retaining atight circumferential grip on the sheath so as to prevent slipping orturning of the sheath, as it is drawn from the welding station 8 andlongitudinally fed into an input end of a plurality of driven reducingrolls 11' included within the sheath reducing station 11.

The driven reducing rolls 11' are adapted to engage the outercircumferential surface of the closed tubular sheath 5' in a manner toprovide reducing forces in a radial direction toward the steel wires 2',and to accurately reduce in a controlled manner the lateral movement ofthe closed tubular sheath 5' from the output end of the caterpillarcapstan 9 to the input side of the draw down station 12. The employmentof driven reducing rolls 11' have been found particularly advantageouswith regard to the processing of closed tubular sheaths having thin wallthicknesses in the range of 0.4 to 0.8 mm.

The draw down station 12 includes a draw down die 12' through which theclose tubular sheath 5' and the cable core 1 (the sheathed cable) arelongitudinally drawn, for example, by a wheel capstan 13, and then fedto a take-up reel 14. Further processing of the sheathed cable maycomprise the application of a plastic covering for corrosion protection.

The cross-sectional view of the partially fabricated cable as depictedby FIG. 3, and the enlarged scale, partial cross-sectional view depictedby FIG. 4, depict the engagement of the inner surfaces of the closedtubular sheath 5' with the outer surfaces of the plurality of twistedsteel wires 2', once such sheath and the core 1 therein have been drawnthrough draw down station 12. As is clearly discernible from FIG. 4, theclosed tubular sheath 5' has a reduced outer circumference, and an innersurface that engages the plurality of steel wires 2' by at leastpartially penetrating the spaces between adjacent ones of the pluralityof the steel wires 2' for achieving a common anchoring of the closedtubular sheath 5' and such steel wires throughout the length of thecable.

Further, in accordance with the instant invention there is achieved across-section of constant volume of the closed tubular sheath 5' once itpasses through the draw down station 12, notwithstanding tolerablethickness variations in the copper strip 5 being drawn from the supplyroller 4. With reference to FIG. 1, there is provided a measuring device15 positioned upstream of the core sheathing station 3 for detectingfluctuations in the thickness of the copper strip 5. Connected betweenthe measuring device 15 and the caterpillar capstan 9 is a servo controlcircuit 16 that controls (after a time delay to compensate for thetravel time of the copper strip 5 from the measuring device 15 to thecaterpillar capstan 9) the longitudinal velocity of the gripperassemblies 10 of the caterpillar capstan 9 to provide an inversedependency. The servo control circuit 16 provides no speed correction tothe caterpillar capstan 9 when the measuring device 15 determines novariance from the nominal thickness of the copper strip 5. Under suchcondition, the gripper assemblies 10 which are in circumferentialengagement with the freshly welded, closed tubular sheath 5', have alongitudinal velocity such as to cause no longitudinal directed pushingor braking force to be applied to the tubular sheath 5'. When themeasuring device 16 detects an increase from the nominal thickness ofthe copper strip 5, the servo control circuit 16 causes a decrease inthe longitudinal velocity of the gripper assemblies 10, thus applying alongitudinal directed braking force to the engaged portions of thefreshly welded, closed tubular sheath 5'. Conversely, when the measuringdevice 16 detects a decrease from the nominal thickness of the copperstrip 5, the servo control circuit 16 causes an increase in thelongitudinal velocity of the gripper assemblies 10, thus applying alongitudinal directed pushing force to the engaged portions of thefreshly welded, closed tubular sheath 5'. In all instances, the tightcircumferential engagement of the gripper assemblies 10 about spacedlongitudinal segments of the tubular sheath 5' assures that thelongitudinally directed braking or pushing forces are applied uniformly,thus avoiding the generation of torsional forces within the freshlywelded, closed tubular sheath 5'. Further, such tight circumferentialengagements prevent torsional forces generated in the freshly welded,closed tubular sheath 5' as it is roll reduced and drawn down onto thesteel wires 2', which are longitudinally stranded over the plurality ofelectrical and optical conductors 2, from being transmitted upstream tothe welding station 8 and the core sheathing station 3. It is ofparticular importance to avoid torsional forces in the copper strip 5 asit is formed into a hollow tube in the core sheathing station 3, sincethe adjacent longitudinal edges to be welded at the welding station 8must be accurately positioned and controlled.

In the circumstance of constant cross-sectional area of the closedtubular sheath 5' at the output side of the draw down station 12, thefollowing equation pertains: ##EQU1## wherein Ve is the velocity of theclosed tubular sheath 5';

Se is the wall thickness of such sheath; and

De is the outer diameter of such sheath, all at the input side of thedraw down station 12.

Accordingly, for a particular outer diameter De, fluctuations in wallthickness Se are balanced inversely by variations in velocity Ve of theclosed tubular sheath 5'.

The longitudinally directed pushing or braking forces per unit of timeto compensate for variations in the wall thickness Se are in accord withthe following proportional relationship: ##EQU2## wherein ΔVe is thevelocity change from the nominal velocity condition; F is thecross-sectional area of the closed tubular sheath 5'; E is thecoefficient of elasticity of the material of which the closed tubularsheath 5' is comprised, in this case copper; and L is the longitudinaldistance between the point of application of the pushing or brakingforces applied to the closed tubular sheath 5' by the gripper assemblies10 and the input of the draw down station 12.

While the invention has been described in connection with an exemplaryembodiment thereof, it will be understood that many modifications willbe apparent to those of ordinary skill in the art and that thisapplication is intended to cover any adaptions or variations thereof.Therefore, it is manifestly intended that the invention be only limitedby the claims and equivalents thereof.

What is claimed:
 1. Method for adjusting the thickness of a hollowtubular member to achieve a cross-section of constant area, comprisingthe steps of:continuously measuring the thickness of a metal strip todetect any increase or decrease thereof from a nominal thickness;continuously drawing the metal strip in a longitudinal direction througha forming means to form a hollow tubular member having a firstcross-section; continuously welding longitudinal abutting edges of thehollow tubular member; continuously engaging and disengaginglongitudinally spaced, circumferential portions of the hollow tubularmember, and applying a longitudinally directed, braking force thereto ifan increase in the thickness of the metal strip is detected, andapplying a longitudinally directed, pushing force thereto if a decreasein the thickness of the metal strip is detected; and continuouslyreducing the hollow tubular member to provide a second cross-sectionwhose area is constant.
 2. Method in accordance with claim 1, furthercomprising the step of circumferentially supporting and longitudinallydriving the hollow tubular member immediately prior to its reduction. 3.Method in accordance with claim 1, wherein said metal strip is formedaround a cable core having an outer dimension less than the innerdimension of the hollow tubular member.
 4. Method in accordance withclaim 3, wherein said step of continuously reducing the hollow tubularmember causes its inner surface to penetrate into outer surfaces of thecable core to provide tangential and longitudinal anchoring between thetubular member and the core.
 5. Method in accordance with claim 3,wherein the cable core is comprised of a plurality of conductors and aplurality of wires stranded around the conductors, and wherein said stepof continuously reducing the hollow tubular member causes its innersurfaces to engage the stranded wires by at least partially penetratingthe spaces between adjacent ones of the plurality of the stranded wiresfor providing tangential and longitudinal anchoring of the tubularmember and the core.
 6. Method in accordance with claim 1 wherein thelongitudinally directed braking or pushing force per unit of time is inproportion to the following: ##EQU3## wherein ΔVe is the differential invelocity from the nominal velocity; F is the area of the cross-sectionof the tubular sheath at the output side of the draw down station; E isthe coefficient of elasticity of the material of which the tubularsheath is comprised; and L is the shortest distance between the point ofapplication of the braking or pushing force and the point of reductionof outer dimensions of the hollow tubular member.
 7. Method inaccordance with claim 4, wherein said step of engaging and disengaginglongitudinal spaced, circumferential portions of the tubular memberincludes tightly circumferentially gripping of the tubular member. 8.Apparatus for adjusting the thickness of a hollow tubular member toachieve a cross-section of constant area, comprisinga source of metalstrip; a means for continuously drawing the metal strip in alongitudinal direction; a measuring means for continuously measuring thethickness of the metal strip to detect an increase or decrease thereoffrom a nominal thickness; a forming means for continuously forming themetal strip into a hollow tubular member having a first cross-section; awelding means for continuously welding longitudinal abutting edges ofthe hollow tubular member; a capstan means for continuously engaging anddisengaging longitudinally spaced, circumferential portions of thehollow tubular member, and applying a longitudinally directed, brakingforce thereto if an increase in the thickness of the metal strip isdetected, and applying a longitudinally directed, pushing force theretoif a decrease in the thickness of the metal strip is detected, saidcapstan means including a plurality of gripper assemblies that move inan elongated endless path; a servo means coupled between said measuringmeans and said capstan means for controlling longitudinal velocity ofsaid gripper assemblies for applying the braking or pushing force to thehollow tubular member; and a draw down means for reducing the hollowtubular member to provide a second cross-section whose area is constant.9. Apparatus in accordance with claim 8, further comprising a pluralityof driven support rollers adapted to circumferentially engage an outersurface of the hollow tubular member for supporting and directing thelongitudinal movement thereof from the output end of said capstan meansto an input side of said draw down means.
 10. Apparatus in accordancewith claim 8, further comprising a source of cable core, said means forcontinuously drawing the metal strip also drawing the cable core in alongitudinal direction, said forming means continuously forming themetal strip around the cable core.
 11. Apparatus in accordance withclaim 10, wherein said draw down means reduces the hollow tubularmember, causing the inner surface thereof to penetrate into outersurfaces of the cable core to provide tangential and longitudinalanchoring between the tubular member and the core.
 12. Apparatus inaccordance with claim 10, wherein the cable core is comprised of aplurality of conductors and a plurality of wires stranded over theconductors, and wherein said draw down means reduces the hollow tubularmember, causing the inner surface thereof to partially penetrate thespaces between adjacent ones of the plurality of stranded wires forproviding tangential and longitudinal anchoring of the tubular memberand the stranded wires.
 13. Apparatus in accordance with claim 8,wherein each of said gripper assemblies provides a tight circumferentialgripping of the tubular member.